/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
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 *
 *
 */
package javax.swing;

import java.awt.*;

import javax.swing.plaf.*;
import javax.accessibility.*;

import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;


/**
 * <code>JPanel</code> is a generic lightweight container. For examples and task-oriented
 * documentation for JPanel, see <a href="https://docs.oracle.com/javase/tutorial/uiswing/components/panel.html">How
 * to Use Panels</a>, a section in <em>The Java Tutorial</em>. <p> <strong>Warning:</strong> Swing
 * is not thread safe. For more information see <a href="package-summary.html#threading">Swing's
 * Threading Policy</a>. <p> <strong>Warning:</strong> Serialized objects of this class will not be
 * compatible with future Swing releases. The current serialization support is appropriate for short
 * term storage or RMI between applications running the same version of Swing.  As of 1.4, support
 * for long term storage of all JavaBeans&trade; has been added to the <code>java.beans</code>
 * package. Please see {@link java.beans.XMLEncoder}.
 *
 * @author Arnaud Weber
 * @author Steve Wilson
 * @beaninfo description: A generic lightweight container.
 */
public class JPanel extends JComponent implements Accessible {

  /**
   * @see #getUIClassID
   * @see #readObject
   */
  private static final String uiClassID = "PanelUI";

  /**
   * Creates a new JPanel with the specified layout manager and buffering
   * strategy.
   *
   * @param layout the LayoutManager to use
   * @param isDoubleBuffered a boolean, true for double-buffering, which uses additional memory
   * space to achieve fast, flicker-free updates
   */
  public JPanel(LayoutManager layout, boolean isDoubleBuffered) {
    setLayout(layout);
    setDoubleBuffered(isDoubleBuffered);
    setUIProperty("opaque", Boolean.TRUE);
    updateUI();
  }

  /**
   * Create a new buffered JPanel with the specified layout manager
   *
   * @param layout the LayoutManager to use
   */
  public JPanel(LayoutManager layout) {
    this(layout, true);
  }

  /**
   * Creates a new <code>JPanel</code> with <code>FlowLayout</code>
   * and the specified buffering strategy.
   * If <code>isDoubleBuffered</code> is true, the <code>JPanel</code>
   * will use a double buffer.
   *
   * @param isDoubleBuffered a boolean, true for double-buffering, which uses additional memory
   * space to achieve fast, flicker-free updates
   */
  public JPanel(boolean isDoubleBuffered) {
    this(new FlowLayout(), isDoubleBuffered);
  }

  /**
   * Creates a new <code>JPanel</code> with a double buffer
   * and a flow layout.
   */
  public JPanel() {
    this(true);
  }

  /**
   * Resets the UI property with a value from the current look and feel.
   *
   * @see JComponent#updateUI
   */
  public void updateUI() {
    setUI((PanelUI) UIManager.getUI(this));
  }

  /**
   * Returns the look and feel (L&amp;amp;F) object that renders this component.
   *
   * @return the PanelUI object that renders this component
   * @since 1.4
   */
  public PanelUI getUI() {
    return (PanelUI) ui;
  }


  /**
   * Sets the look and feel (L&amp;F) object that renders this component.
   *
   * @param ui the PanelUI L&amp;F object
   * @beaninfo bound: true hidden: true attribute: visualUpdate true description: The UI object that
   * implements the Component's LookAndFeel.
   * @see UIDefaults#getUI
   * @since 1.4
   */
  public void setUI(PanelUI ui) {
    super.setUI(ui);
  }

  /**
   * Returns a string that specifies the name of the L&amp;F class
   * that renders this component.
   *
   * @return "PanelUI"
   * @beaninfo expert: true description: A string that specifies the name of the L&amp;F class.
   * @see JComponent#getUIClassID
   * @see UIDefaults#getUI
   */
  public String getUIClassID() {
    return uiClassID;
  }


  /**
   * See readObject() and writeObject() in JComponent for more
   * information about serialization in Swing.
   */
  private void writeObject(ObjectOutputStream s) throws IOException {
    s.defaultWriteObject();
    if (getUIClassID().equals(uiClassID)) {
      byte count = JComponent.getWriteObjCounter(this);
      JComponent.setWriteObjCounter(this, --count);
      if (count == 0 && ui != null) {
        ui.installUI(this);
      }
    }
  }


  /**
   * Returns a string representation of this JPanel. This method
   * is intended to be used only for debugging purposes, and the
   * content and format of the returned string may vary between
   * implementations. The returned string may be empty but may not
   * be <code>null</code>.
   *
   * @return a string representation of this JPanel.
   */
  protected String paramString() {
    return super.paramString();
  }

/////////////////
// Accessibility support
////////////////

  /**
   * Gets the AccessibleContext associated with this JPanel.
   * For JPanels, the AccessibleContext takes the form of an
   * AccessibleJPanel.
   * A new AccessibleJPanel instance is created if necessary.
   *
   * @return an AccessibleJPanel that serves as the AccessibleContext of this JPanel
   */
  public AccessibleContext getAccessibleContext() {
    if (accessibleContext == null) {
      accessibleContext = new AccessibleJPanel();
    }
    return accessibleContext;
  }

  /**
   * This class implements accessibility support for the
   * <code>JPanel</code> class.  It provides an implementation of the
   * Java Accessibility API appropriate to panel user-interface
   * elements.
   * <p>
   * <strong>Warning:</strong>
   * Serialized objects of this class will not be compatible with
   * future Swing releases. The current serialization support is
   * appropriate for short term storage or RMI between applications running
   * the same version of Swing.  As of 1.4, support for long term storage
   * of all JavaBeans&trade;
   * has been added to the <code>java.beans</code> package.
   * Please see {@link java.beans.XMLEncoder}.
   */
  protected class AccessibleJPanel extends AccessibleJComponent {

    /**
     * Get the role of this object.
     *
     * @return an instance of AccessibleRole describing the role of the object
     */
    public AccessibleRole getAccessibleRole() {
      return AccessibleRole.PANEL;
    }
  }
}
